Solar USB Charger

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Introduction: Solar USB Charger

About: I am a graduate student in conservation biology at Clemson University. When I'm not studying in the library or out in the field collecting data, I love designing and building DIY projects!

This 3D printed solar USB charger is inexpensive and easy to make. It's compatible with almost any device that charges via USB. In direct sunlight it is capable of charging the internal battery at about 500 mah, and can deliver 1000 mah to devices. Here's the tools and supplies you'll need:

Tools:

  • Fine tip soldering iron and solder
  • Epoxy or super glue
  • Scissors or wire cutters

Supplies:

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Step 1: About the Components

Here's the details for the components used in this project:

Solar Panel:

The AllPowers 2.5 watt solar panel is among the best available on Amazon. It produces about 6.2v open circuit and 5.6v under load at up to 500 mah in full sunlight. For this project I used an inline 1N4001 blocking diode to keep the panel from discharging the battery. The 1N4001 can handle up to 1 amp continuous current and drops the voltage about 0.7v, which is perfect for the input on the charging board.

Adafruit PowerBoost 500 Charger:

The PowerBoost 500 is a dual Li-Poly charger and DC/DC boost board. It charges lithium ion and polymer batteries at a rate of 500mah (perfect for the solar panel in this project) and outputs 5.2v at up to 1 amp to charge devices. It allows for simultaneous battery charging and load. It has an easy to read pinout and connections for an external power switch. Because the power switch doesn't carry the circuit's current load, almost any switch or button can be used. For this project I used a single 18650 battery, but the board will charge many types of single cell batteries. It has a battery management system (BMS) with over-charge, over-discharge, and over-current protection. There are cheaper battery charging boards (TP4056) and DC/DC boost boards available, but the quality of the Adafruit board ensures that it will be safe to use when charging expensive devices!

Step 2: Printing the Enclosure

The 3D printed enclosure for this project is available below as an .stl file. The outside dimensions are 160mm by 140mm by 39mm tall. The rim is 6.5mm thick and has a 2.5mm wide inset for the solar panel. The solar panel sits flush with the top of the enclosure and acts as the lid for the solar charger. The front of the enclosure has a 20mm through hole for the panel mount USB port and a 13mm through hole for the power button. There are also internal guides for the PowerBoost board and the battery holder.

I sliced the model in Cura 4.3 using the recommended settings for high detail:

  • 0.2mm layer height
  • 20% grid infill
  • 30mm/s printing speed
  • 0.5mm wall thickness
  • Brim type skirt and automatic support generation

I printed the enclosure on a Lulzbot TAZ 6 in 2.85mm PLA, but most 3D printers should be able to handle this print (just make sure the print bed is large enough). If you don't have a 3D printer, the .stl file can be uploaded to Treatstock.com (a 3D printing service) and printed/mailed for about $20 USD. The print takes approximately 8 hours and uses 170g of material. I used a 205C nozzle and 60C bed temperature.

Step 3: Preparing the USB Port

The Batige panel mount USB port makes installing the charging port simple and secure. The part on Amazon comes with a 1m cable that ends in a male USB plug. I cut the cable at about 15cm and exposed the leads so they could be soldered directly to the charging board. The cable has a silver shield that contains four wires:

  • Red: +5v
  • Black: Ground
  • White: Data +
  • Green: Data -

iPhones and a few other devices require a certain voltage across the data pins before the device will recognize a power source and begin charging. Most other devices only require +5v and a ground. If you plan to use this solar charger for Apple products, you'll need to wire the data + and data - pins from the USB port to the board.

Step 4: Wiring the Components

There are four parts that need to be connected to the charging board: the battery, power button, solar panel, and USB port. The wiring diagram above shows how to connect all the components together. All the pins on the charging board are labelled. The solar panel acts as a lid for the enclosure, so be sure to cut the wires long enough to accommodate moving the panel around before it is glued in place. Notice the orientation of the diode in the diagram (the gray end points towards the charging board). The board uses a common ground, so all pins labelled GND are connected and can be used interchangeably.

  • The solar panel connects to the USB (+) and GND (-) pins with the diode inline on the + wire
  • The power button connects to the EN and GND pins, which wire goes where doesn't matter
  • The battery connects to the Bat (+) and GND (-) pins
  • The USB port connects to the USB + (+) and USB - (-) pins on the right side of the board
  • The D+ (green) and D- (white) wires connect to the right side of the board if needed

AN IMPORTANT NOTE: Because the USB port and the power button are installed in through holes in the enclosure, remember to run the wires through the holes before soldering them to the board!

Step 5: Installing the Components

Once all the components are wired together, they can be installed in the enclosure. Use epoxy or super glue to secure the PowerBoost and the battery to the bottom of the enclosure. There is plenty of room to accommodate different battery shapes and sizes.

Push the panel mount USB port into the through hole. It has tabs that lock it into place. Add a little bit of glue or epoxy to make sure its secure and to keep the USB port horizontal in the enclosure.

Thread the power button into the other through hole and tighten the nut on the back. As with the USB port, add a little glue or epoxy to make sure it isn't going anywhere.

I also glued the diode to the underside of the solar panel and added glue over the soldered wires for extra durability.

Step 6: Testing and Final Assembly

Now that everything is wired together and glued in place, the solar charger can be tested. The PowerBoost has four LED indicators that make testing easy.

  • Blue: indicates that the boost converter is active and producing 5v
  • Red: indicates low battery (3.2v)
  • Yellow: indicates that the battery is being charged
  • Green: indicates when the battery is fully charged (4.2v)

First you'll want to test whether the solar panel can charge the battery. To do this, aim the solar panel at the sun and check to see if the yellow indicator light is on. This means that power from the panel is being sent to the PowerBoost, and that the PowerBoost is charging the battery.

Second, you'll want to make sure the PowerBoost can charge your devices (and that the power switch is functional). To do this, press the power button and you should see the blue indicator LED light up. Press the button again and it should go out. If the switch doesn't work, the charger board will continuously draw power from the battery even when no device is being charged. If the indicator is on, plug in a device via the USB port and make sure it is actively charging.

If everything works the way it should, then the solar charger is ready for final assembly. Simply apply a bead of epoxy or some super glue to the rim of the enclosure and press the solar panel into place, making sure that it is flush all the way around and not squishing any wires underneath. That's it! You now have a fully functional solar charger for all your devices.

Step 7: Adding a Personal Touch

This project is designed around a specific solar panel, but can be modified in many ways to suit your needs and design ideas! The enclosure file is in a .stl format. This file type can be opened and modified using almost any design software, including TinkerCAD, which is available online for free.

The PowerBoost board can accommodate many shapes and sizes of batteries, many types of power buttons, and many inputs. With this in mind, you could:

  • Change the diameter of the through hole for the USB port to incorporate other output port types like USB C or a barrel jack
  • Change the diameter of the through hole for the power button to suit your own power button or toggle switch
  • Change the dimensions of the enclosure for a different sized solar panel
  • Make the enclosure super thin by using a flat lithium polymer battery instead of an 18650 cell
  • Add a power indicator by connecting an LED and resistor to the 5V and GND pins, or use a power button with a built in LED

If you have any questions or ideas, feel free to leave a comment at the bottom of the page. Thanks for reading, and good luck building!

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    2 Discussions

    0
    smcmasters1
    smcmasters1

    Question 8 weeks ago

    I don't know jack, nor understand a lick about the amps or voltage- but suppose I had 4× 18650 batteries that I wanted to use for this project- would I use the same diode? And would the Powerboost 500 still be efficient?

    0
    bcschmi6
    bcschmi6

    Answer 8 weeks ago

    The same diode can be used with any battery. The PowerBoost 500 is designed to charge single cell batteries at a rate of 500 mah. You could use 4 18650 cells as long as you combine them in parallel into a single 3.7v battery (Make sure you read about how to properly connect multiple 18650 cells in parallel). Just remember that the max charge rate of the PowerBoost is 500 mah, so if you make a large battery pack it will take proportionally longer to charge.